1. Field of the Invention
The present invention relates to an apparatus and a method for disinfecting water by the direct injection of gaseous ozone into the water. More particularly, the present invention relates to a water treatment apparatus and a method in which gaseous ozone is injected into an auxiliary feedstream of water, which is then introduced at several spaced and distinct points in the flow path of the water to be treated, in order to provide sequential and multiple exposures to ozone of the water to be treated.
2. Description of the Related Art
The notion of treating water with gaseous ozone for disinfection is well known. Various types of apparatus and methods have been devised to dissolve gaseous ozone into water for treatment of the water by providing retention chambers in which the ozone is introduced through mechanical mixers, injectors, porous diffusers, and packed columns. The primary purpose of each of those approaches is to transfer sufficient gaseous ozone to the water to be treated, in order to provide as large as possible contact of the water with the ozone so that the disinfection treatment is as thorough as possible.
Although there are several known approaches to accomplish the disinfection operation, even the more efficient of those processes, in terms of the efficiency of exposure of the water to ozone, include certain drawbacks. For example, although packed column technology provides transfer efficiencies of from about 80% to about 95%, there is little operational experience with such approaches, and, more significantly, there is a strong potential for high head losses as the result of build-up of scale on the column medium.
Mechanical mixing, on the other hand, although capable of providing ozone transfer rates in the range of from about 90% to about 98%, involves short contact times that might require retreatment, and also involves high operating cost because of the energy and maintenance requirements.
Bubble diffuser contactors are quite widely used, and provide ozone transfer efficiencies in the range of about 85% to about 95%. However, very large contact vessels are required, to accommodate the diffuser layout, and diffuser plugging is a common problem. The uniform distribution of gaseous ozone across the diffuser grid of the contactor is also a problem at low gas flow rates, sometimes resulting in inadequate disinfection of the water being treated.
Direct injection of ozone has distinct advantages in terms of low energy and maintenance costs, but heretofore ozone transfer efficiencies were only on the order of about 70%.
It is an object of the present invention to overcome the deficiencies in the previously-employed apparatus and methods.
It is a further object of the present invention to provide a water treatment apparatus and method utilizing direct injection of ozone and that results in improved ozone transfer efficiency.
It is another object of the present invention to provide an apparatus and method for direct injection of ozone in combination with multiple contact chambers that can be used for providing primary disinfection of potable water to meet surface water treatment regulations issued by the United States Environmental Protection Agency.